This pattern shows that the speaker (or someone else) does an action for another person's benefit. It's often translated as 'do (something) for (someone)'. For example, if you help a friend move, you can say 手伝ってあげた. The person receiving the favor is marked with に, but it's often omitted if clear from context.

In everyday conversation, あげる is frequently shortened to あげる (but in casual speech, it may sound like あげる, not a contracted form). Be careful: using てあげる when the favor is not requested or when the receiver is a superior can sound presumptuous or rude. For example, telling your boss '手伝ってあげます' would imply you're doing them a favor, which is inappropriate. In such cases, use ましょうか or another humble form.

This pattern is more common in casual or friendly contexts. In formal writing or polite speech, you might see さしあげる instead, but that's very formal and rarely used in modern conversation.